Concreate, Inc. delivers concrete polishing and custom staining for both commercial and residential projects primarily in Virginia and Maryland (but also up and down the East Coast). We work hand in hand with with designers, architects, project managers, general contractors, tradesmen, and home owners alike from start to finish. We welcome the opportunity to serve your polished concrete needs in every way possible.

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The Difference Between Joint Filling and Joint Sealing

The Difference Between Joint Filling and Joint Sealing

Joints in a concrete floor.

They’re icky and they’re sticky. Selecting one is tricky. It’s why the pros are picky. Explore them with Concreate!

Key Takeaways:

  • Concrete sealers and fillers can help fill joints
  • Sealers are soft, flexible, and waterproof
  • Fillers are hard and strong
  • The option you choose will depend on how your concrete floor will be used

Want your concrete floor to successfully survive cold snaps without cracking? Looking for super-strong structural support that won’t buckle under pressure? Maybe you don’t know that concrete-chomping bacteria are out to feast on your floor (it’s news to most people).

If any of those apply to you, then you need to read this guide on how to choose between joint filling and joint sealing! Both are used to fill joints in concrete, and both have their own ways of doing it.

The problems concrete joint sealing can solve

Sealers are a contractor’s flexible friend and come in various caulking types like polyurethane, butyl, silicone, and acrylic. Softer than fillers and more cooperative with shifts in environmental temperatures, sealers are elastomeric and can help joints handle the freeze-thaw cycle in ways fillers can’t.

This cycle is bad for concrete and starts when water works its way into the slab. Moisture can freeze and expand, putting pressure on the rigid concrete’s tensile strength. The concrete, being tough, doesn’t want to give. This can cause cracks in the surface and create inlets for even more moisture to enter when thawing finally occurs.

Along with that water can come dirt, debris, and even bacteria to weaken the concrete, all of which could also be blown into cracks by the wind, making air yet another threat. There really are bacteria out there tough enough to take down concrete. One of them is called Bryobacter, which can contribute to a condition termed concrete cancer,” currently being researched. And yes, it’s as nasty as it sounds.

Joint sealing types and areas of use

Joint sealers come in pre-formed or liquid-applied types and are either pourable or loaded into the biggest caulking gun you’ve ever seen. They’re most often used in outdoor applications where concrete is much more vulnerable to the elements and shifting seasons. The ASTM C 920 classifies them as good to fill joints in concrete on buildings, plazas, and decks for pedestrian or vehicular use.

Choosing the right material for joint sealing will differ based on the location it will be applied in and on factors such as substrate type and the amount of expected joint movement. Of course, none of this answers the big question: whether El Astomeric will beat Bry O’ Bacter in a straight fight. It’s still under scientific review, but we’re rooting for the first guy.

How a good sealer (and concrete sealer slinger) behaves

Joint sealing should only occur after the slab has finished shrinking – a natural part of the curing process as water evaporates from the slab. This leaves some cracks in the surface, which again is natural with drying concrete. When the cracks appear, the sealant can be strategically applied.

A backing rod is placed into the joint to give the sealer its signature “hourglass” shape. This lets the joint sealer handle the expansion and contraction that comes with the freeze-thaw cycle, relieving the pressure on the slab and reducing the chances of surface cracking.

Joint sealing provides a barrier against moisture, debris, and microorganisms while also doing its part to prevent soil erosion which can cause slabs to destabilize. You can learn more about slab stabilization from the experts on our This is Concrete podcast.

A high-quality sealer will cling to concrete like white on rice, stretching and relaxing with the slab and cushioning the joint as surrounding temperatures change. It should also offer some degree of protection against water intrusion beneath the concrete. Joint sealing shouldn’t need to be repeated frequently; an annual assessment and fix are often enough to provide long-lasting service.

Joint filling: The low-jiggle solution

Contractors use joint fillers when strength and firmness are needed more than flexibility. They’re usually applied indoors and allow very little to no movement in the joint, so the edges of the concrete can safely support a lot of weight. Fillers, therefore, aren’t as supple as sealers, nor do they supply the latter’s high level of tensile and bonding strength.

On the plus side, they are highly shock absorbent. This is very handy when it comes to protecting concrete slab edges or central lines being laid around the heavy-duty machinery and processes of a construction site. Whack a joint sealer with a forklift or a dolly, and it’s game over. Long-term, joint fillers also protect edges from chipping and spalling, which is when concrete becomes flaky and weak.

Joint fillers are usually made of polyurea, silicone, or epoxy, with epoxy being more chemical resistant, whereas silicone is highly water resistant. Fillers are only applicable when deeply installed into saw-cut control joints, thus named because they help contractors manage where cracks will appear as newly laid concrete starts to shrink. Saw cuts must be made to shallow precision depths and with proper timing, while the slab is strong enough to support them but hasn’t started cracking on its own yet.

Joint fillers are carefully mixed with water during application and usually cure much faster than joint sealers. Each material should be inspected at least once every year to make sure they’re holding up. Both should last you at least a few years, with higher-grade silicone mixes lasting even longer than that. It’s all in how professionally they’re mixed, applied, and maintained.

Contact the Concreate team with any questions

If you have to fill joints in concrete, choose joint sealing if you want to give your slab some flexing room. Choose joint filling when you want a firm set of tough, load-bearing edges.

Successfully applying joint fillers and sealers takes skilled contractors with specialized tools and equipment, so don’t entrust the job to just anybody. You can contact our team to learn more about why Concreate’s expert contractors are the pros to turn to!